1. Field of the Invention
The present invention relates to a flexible metal clad laminate and a manufacturing method thereof, and more particularly, to a flexible metal clad laminate obtained by heating polyamic acid which is a polyimide precursor at a high temperature and transforming into final polyimide, and a manufacturing method thereof.
2. Description of the Related Art
A flexible metal clad laminate used for manufacturing a flexible printed circuit board is a laminate of a conductive metal foil and an insulating resin. The flexible metal clad laminate may be processed to fine patterned circuits and bended in a narrow space. According to the trend of small sized and light weight electronic devices, the application field of the flexible metal clad laminate has been increased in a notebook computer, a portable information terminal, a small-sized video camera, a disk for storage, etc.
The flexible metal clad laminate concerning the above-described technique may be generally manufactured by a method of laminating a thermoplastic polyimide film on a polyimide film with a conductive metal foil, or a casting method including directly coating a polyamic acid solution, which is a polyimide precursor, on a metal foil. In the casting method, a heating process with a high temperature is necessary for conversion of the polyamic acid into polyimide. The casting method for manufacturing of the flexible metal clad laminate may be classified into a roll-to-roll process and a batch process according to a curing method.
In the batch process, pre- and post-processes are necessary for preventing adhesion generated between the metal foil and the polyimide during the batch curing. In addition, the batch process had a bad productivity because the length for treatment per roll is required to be short.
In the roll-to-roll process, a polyamic acid solution, a polyimide precursor, is coated on a metal foil and dried. After that, it is unrolled and the thermal curing is conducted before rewinding process. The roll-to-roll process can reduce the production time and cost, therefore, it can overcome the disadvantage of batch process which had a low productivity. However, the roll-to-roll curing is conducted during a short time. Thus, a rapid heating rate may cause defects such as blistering, delamination, a wrinkling phenomenon due to a rapid contraction/expansion, etc. These defects may be reduced by decreasing the line speed, but this can also reduce the productivity.
In general, a flexible metal clad laminate consists of one or more polyimide layers. In order to increase the productivity, a metal clad laminate of one polyimide layer may be manufactured. A metal clad laminate of two or more polyimide layers may prevent warpage and curl between a metal foil and the polymer film and may increase adhesion strength, mechanical properties, electrical properties, etc.
When manufacturing a flexible metal clad laminate using polyimide film with two or more layers, a polyimide resin making a contact with a metal foil and having a glass transition temperature of 300° C. or over may be used to restrain the generation of appearance defects after heating, as disclosed in Korean Patent Publication Nos. 10-2010-0048474 and 10-2010-0127125. However, the above-described flexible metal clad laminate has a low bonding strength with an anisotropic conductive film (ACF) used in a liquid crystal display or a touch screen, etc.